1. Field of the Invention
The present invention relates to protective coatings for thin films of metals, such as silver or aluminum, a combination of silver and copper, or the like, which are applied to substrates. More specifically, the present invention relates to pretreatment compositions for thin metallic films, such as silver, which are applied to substrates such as glass.
2. Brief Description of the Prior Art
It is known in the art to deposit thin metallic films on substrates for functional and/or aesthetic reasons. For example, thin films of silver are deposited on glass to produce mirrors or other reflective surfaces for purposes such as energy conservation. Depending on the intended use, the thin metallic films may vary widely in thickness. For example, the metallic films on mirrors typically vary in thickness and range from about 3 to about 10 microinches (from about 76.2 to about 254 millimicrons) whereas partially reflective metallic films on windows, where the films serve as solar reflectors, vary in thickness and range from about 4.times.10.sup.-8 inches to about 20.times.10.sup.-8 inches (about 1 to about 5.1 millimicrons).
To preserve the integrity of the thin metallic films, protective materials in the form of, say, additives, pertinent among which are corrosion inhibitors, are employed therewith. Conventionally, protective materials, typically incorporated in coatings, are applied to the back of the metallic films. This mode of application is herein denoted as a "conventional" application. In contrast, the protective materials of this invention are applied as pretreatment compositions.